Characterization of the products of the thermal decomposition of Mm(OH)3 mischmetal hydroxide by various TEM techniques

E. ZELAYA; M.R ESQUIVEL; D. SCHRYVERS

ACTA MICROSCOPICA

Instituto Venezolano de Investigación Científica

Lugar: Caracas, Venezuela; Año: 2010 vol. 18 p. 249 - 250

0798-4545

In this work, manifold Transmission Electron microscopy (TEM) techniques were used to analyze the chemical composition and crystalline structures occurring during the thermal decomposition and further mechanical milling of Mischmetal-based hydroxide (Mm(OH3)).  The Lanthanide composition of the starting hydroxide, La0.25Ce0.52Nd0.17Pr0.06(OH)3, was done using XEDS. The results were compared to those obtained using Neutron Activation Analysis (NAA) and Energy Dispersive Spectroscopy (EDS) microanalysis.  The hydroxide is thermally unstable and looses water on heating according to: Mm(OH)3 (T<50 ºC)    ®     MmOOH (T<100 ºC)    ®  MmO2 After this heating cycle, the initial structure was recovered by mechanical milling plus aging in air. The crystalline structures of these compounds were determined at micro and nano-scale using a combination of calculations on TEM diffraction patterns and Rietveld analysis on XRD measurements.   Hexagonal Mm(OH)3 is described by P6/3m space group. Intermediarie MmOOH occurs in the monoclinic system and MmO2 structure is assigned to Fm3m space group. Chemical segregation on MmO2 was found after mechanical milling. The segregation was identified by different contrast obtained with high-angle annular dark field (HAADF) image of the scanned particles. This result was also confirmed by the compositional determination of the different contrast areas of the particles by XEDS.